Studies will be conducted to define the mechanisms by which changes in hemodynamic variables induce changes in release of ACTH in the pituitary and, thus, changes in adrenal secretion of cortisol. Special attention is directed to the definition of anatomical and functional organization of central nervous components subserving the pituitary adrenal response to hemodynamic change. Other studies are directed to the investigation of feedback inhibition and of physiologic facilitation which follow an initial stimulus and which may modulate the response to a subsequent stimulus. The relations among pertinent factors will be studied and attention will be directed to the temporal and quantitative features of the responses of pituitary and adrenal to hemodynamic mechanisms. The interaction of the system mediating the pituitary adrenal response to hemodynamic changes and those mechanisms subserving the response of this system to other stimuli will be studied. Finally, the role of cortisol in mediation of restitution of plasma volume will be defined. The results will be incorporated in a comprehensive description of the function of the system to extend previous descriptions.